Coating composition, based on organically modified inorganic condensates

ABSTRACT

A coating composition comprises a polycondensate obtained by reacting a prehydrolysate based on at least on epoxide-containing hydrolysable silane; at least one amine component selected from a prehydrolysate based on at least one amino-containing hydrolysable silane and an amine compound containing at least two amino groups; and an amino group protective reagent. The coating composition is particulary suitable for coating glass, glass ceramic, ceramic, and plastic, and permits an increase in strength and protection against damage.

The present invention relates to a coating composition comprisingorganically modified inorganic condensates based on hydrolysable silanescontaining at least one epoxide group, to a process for preparing thecoating composition, to the use thereof for coating substrates,especially glass, and to substrates coated therewith.

The fracture strength of glass is drastically reduced by surfacemicrocracks, so that the actual strength is lower by several orders ofmagnitude than the theoretical strength. These microcracks come about asa result of mechanical, thermal and/or chemical attack on the surface ofthe glass during production and processing, but also in the course ofuse.

It is known that the fracture strength of damaged glass can be increasedfurther by coating, filling the microcracks with a transparent glasslikesol-gel material and/or using the coating process to produce a zone ofcompressive strain in the near-surface region of the glass. Studies arealso known which use glass ceramic coats, metal oxide coats or elseceramic coats for increasing the strength. In general, however, thesecoats lack glasslike transparency, which limits their use.

It has also been found to be the case that, although these glasslike orceramic-like coats are able to increase the fracture strength, they areunable to protect the glass against renewed damage, since their brittlefracture properties are similar to those of the underlying glass surfaceto which they are firmly bonded chemically via oxygen bridges. As aresult, under external attack, similar damage is produced in the coatingand can propagate into the glass. The same applies to applied coats ofan SiO₂ sol-gel, irrespective of whether the coats used are thick orthin, in the μm range.

One widespread protection for glass in terms of the strength propertiesis that known as cold end coating with waxes, fatty acids or fatty acidesters, which is described, for example, in U.S. Pat. No. 4,232,065.Further possible treatments include the application of thin polymercoats with thicknesses of about 8 μm, as described in WO 93/6054, or theuse of polysiloxane-containing wax, fatty acid or fatty acid estercoats, which are disclosed in WO 98/45217.

In order both to retard the rapid drop in strength mentioned at theoutset and to obtain protection against mechanical damage in combinationwith sufficient slip properties, WO 97/41966 proposed coating the glasswith organic polymer coats. This is done by applying polymer coats witha thickness of 80-100 μm using, for example, a powder coating material.Protection against stress cracking corrosion, however, is difficultowing to the high water permeability. Water diffuses to thepolymer/glass interface where, owing to the weak attachment of thepolymer, it causes the known, strength-lowering corrosion phenomena. Afurther grave disadvantage when using thick polymer coats is thatrecovery of the glass necessitates a very cumbersome procedure toseparate glass from polymer, in order not to disrupt the redoxequilibrium in the glass melting furnace. With polymer-coated bottles,for instance, the shards are ground to a particle size within the rangeof the polymer coat thickness (50 μm-100 μm) and the polymer fraction isseparated off by agitation.

The object on which the invention was based was therefore to provide acoating having a high strength-maintaining effect without adverselyaffecting the recyclability of glass. A further requirement was, on theone hand, to achieve effective adhesion to the glass while, on the otherhand, avoiding the brittleness of ceramic materials and at the same timeobtaining sufficient abrasion strength.

The object according to the invention, with the diverse and divergentrequirements, has surprisingly been achieved by means of a coatingcomposition comprising a polycondensate obtainable by reacting

a) a prehydrolysate based on at least one hydrolysable silane having atleast one nonhydrolysable substituent, the silane containing one or moreepoxide groups on at least one non-hydrolysable substituent;

b) at least one amine component selected from (1) prehydrolysates basedon at least one hydrolysable silane having at least one nonhydrolysablesubstituent, the silane containing one or more amino groups on at leastone nonhydrolysable substituent, and (2) amine compounds containing atleast two amino groups, and

c) an amino protective group reagent.

The invention provides coating compositions which can be used toincrease the fracture strength of glass, especially damaged glass. Atthe same time, high abrasion-resistant coatings are obtained which,moreover, adhere effectively to glass. Nor do any problems arise withregard to the recovery of the glass.

The prehydrolysate used as component a) is based on at least onehydrolysable silane having at least one nonhydrolysable substituent, thesilane containing an epoxide group on at least one nonhydrolysablesubstituent. This silane is a silicon compound having from 1 to 3,preferably 2 or 3, with particular preference 3, hydrolysable radicalsand 1, 2 or 3, preferably 1 or 2, with particular preference one,nonhydrolysable radical(s). At least one of the nonhydrolysable radicalspossesses at least one epoxide group.

Examples of nonhydrolysable radicals R containing epoxide group are inparticular those which possess a glycidyl or glycidyloxy group. They canbe linked to the silicon atom by way of an alkylene group, e.g. a C₁-C₆alkylene, such as methylene, ethylene, propylene or butylene. Specificexamples of hydrolysable silanes that can be used in accordance with theinvention can be found, for example, in EP-A-195493. Examples ofnonhydrolysable radicals without epoxide groups are the examples of theradical R″ that are listed below for the general formula (III). Examplesof hydrolysable radicals are the examples of the radical X that arelisted below for the general formula (I).

Hydrolysable silanes with epoxide group that are particularly preferredin accordance with the invention are those of the general formula (I):

X₃SiR  (I)

in which the radicals X, the same as or different from one another(preferably identical), stand for a hydrolysable group and are, forexample, a halogen (F, Cl, Br and I, especially Cl and Br), alkoxy(especially C₁₋₄ alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxyand butoxy), aryloxy (especially C₆₋₁₀ aryloxy, e.g. phenoxy), acyloxy(especially C₁₋₄ acyloxy, such as acetoxy and propionyloxy) andalkylcarbonyl (e.g. acetyl), and R is a nonhydrolysable group containingat least one epoxide group, e.g. an aliphatic, cycloaliphatic oraromatic group, in particular an alkylene group, e.g. a C₁-C₆ alkylene,such as methylene, ethylene, propylene and butylene, containing at leastone epoxide group. The radical X is preferably C₁₋₄ alkoxy and withparticular preference methoxy and ethoxy, and R is preferably aglycidyloxy-(C₁₋₆)-alkylene radical.

Owing to its ready availability, γ-glycidyloxypropyltrimethoxysilane(abbreviated below to GPTS) is used with particular preference. Furtherexamples are glycidyloxypropyltriethoxysilane,glycidyloxypropylmethyldiethoxysilane andglycidyloxypropylmethyldimethoxysilane.

Component b) comprises at least one amine component selected from (1)prehydrolysates based on at least one hydrolysable silane having atleast one nonhydrolysable substituent, the silane containing an aminogroup on at least one nonhydrolysable substituent, and (2) aminecompounds containing at least two amino groups. Components (1) and (2)can be used alone or in a mixture. Component b) is preferably composedat least in part of component (1); for example, at least 20 mol % or atleast 40 mol %, preferably at least 60 mol %, of component b) arecomponent (1). With particular preference, component b) consists only ofcomponent (1).

Component (1) comprises prehydrolysates based on at least onehydrolysable silane having at least one nonhydrolysable substituent, thesilane containing one or more amino groups on at least onenonhydrolysable substituent. The silane has in particular from 1 to 3,preferably 2 or 3, with particular preference 3, hydrolysable radicalsand 1, 2 or 3, preferably 1 or 2, with particular preference one,nonhydrolysable radical(s). At least one of the nonhydrolysable radicalspossesses at least one amino group.

Examples of nonhydrolysable radicals containing at least one amino groupare listed below. Examples of nonhydrolysable radicals without aminogroups are the examples of the radical R″ that are listed below for thegeneral formula (III). Examples of hydrolysable radicals are theexamples of the radical X that are listed above for the general formula(I).

Preferred aminosilanes are those of the general formula (II):

X₃SiR′  (II)

in which the radicals X are defined as in the case of the generalformula (I) above and R′ is a nonhydrolysable, Si-bonded radical whichcontains at least one primary, secondary or tertiary amino group. Theradical R′ can comprise one, two or more amino groups. R′ can, forexample, be —Z—NR¹R², in which Z is an alkylene, e.g. a C₁-C₆ alkylene,such as methylene, ethylene, propylene and butylene, an arylene, e.g.phenylene, or a radical derived from alkylaryl or aralkyl, and R¹ and R²are the same or different and are hydrogen, alkyl, e.g. C₁-C₆ alkyl,such as methyl, ethyl, propyl and butyl, aryl, alkylaryl or aralkyl. R¹and R² may also be linked to one another to form a ring containingnitrogen. Where appropriate, Z, R¹ and R² have one or more customaryorganic substituents. R¹ and/or R² may also be the group —Z′—NR′¹R′², inwhich Z′ is defined like Z and R′¹ and R′² are defined like R¹ and R².Z′ and Z and also R′¹, R′² and R¹, R² may each be the same or differentin the same radical. In this way radicals R′ having two, three or moreamino groups are obtained.

Specific examples of silanes of this kind are3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,N-2-aminoethyl)-3-aminopropyltrimethoxysilane,N-[N′-(2′-aminoethyl)-2-aminoethyl]-3-aminopropyltrimethoxysilane,N-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazole and[N-(2-aminoethyl)-3-aminopropyl]methyldiethoxysilane.

Component (2) comprises amine compounds containing at least two aminogroups. The amino groups can in particular be primary or secondary aminecompounds. Nitrogen compounds of this type may be selected, for example,from aliphatic di-, tri- or tetraamines having from 2 to 8 carbon atoms,N-heterocycles, amino-functional phenols, and polycyclic or aromaticamines. Specific examples are ethylenediamine, diethylenetriamine,triethylenetetramine, 1,6-diaminohexane, 1,6-bis(dimethylamino)-hexane,tetramethylethylenediamine, N,N,N′,N″,N″-pentamethyldiethylenetriamine,1,4-diazabicyclo[2.2.2]octane, cyclohexane-1,2-diamine,2-(aminomethyl)-3,3,5-trimethylcyclopentylamine,4,4′-diaminocyclohexylmethane, 2-methylimidazole, 2-phenylimidazole,1,3-bis(aminomethyl)cyclohexane, bis(4-amino-3-methylcyclohexyl)methane,1,8-diamino-p-menthane, 3-(aminoethyl)-3,3,5-trimethylcyclohexylamine(isophoronediamine), piperazine, piperidine, urotropine,bis(4-aminophenyl)methane and bis(4-aminophenyl) sulphone. Preferredexamples are diethylenetriamine, triethylenetetramine orisophoronediamine.

The amino protective group reagent is a compound containing a functionalgroup which can be reacted with an amino group. In particular, thefunctional group of the amino protective group reagent possesses ahigher reactivity for the amino group than does an epoxide group.Consequently, free amino groups still present in the mixture reactpreferentially with the amino protective group reagent. As a result, aderivatized amine is formed which is no longer available forcrosslinking. The compounds in question may comprise, for example, acidhalides or acid anhydrides, e.g. carboxylic anhydrides, carbonyl halidesor sulphonyl halides. The halides may comprise the acid chloride,bromide or iodide, the acid chlorides being preferred. The compounds inquestion may comprise anhydrides or halides of straight-chain orbranched aliphatic, cycloaliphatic or aromatic carboxylic acids, e.g.anhydrides and halides of C₁-C₈ alkylcarboxylic acids, such as aceticacid, propionic acid, butyric acid and malonic acid, C₁-C₈alkenylcarboxylic acids, such as maleic acid, or C₆-C₂₅ arylcarboxylicacids, such as phthalic acid. Specific examples are propionyl chloride,acetyl chloride, sulphonyl chloride, maleic anhydride, phthalicanhydride and acetic anhydride. In this context, acetic anhydride andacetyl chloride are particularly preferred.

Besides the hydrolysable compounds of components a) and b), otherhydrolysable compounds (component d) may also be used for theconstruction of the inorganic matrix. These compounds are preferablyadded during the formation of component a). However, they can also beadded together with the other components mentioned, b) and c), or as aseparate component, in hydrolysed and/or condensed form.

Hereinbelow, other hydrolysable compounds are understood to be thosewhich are not a hydrolysable silane containing at least one epoxidegroup or one amino group. These other compounds likewise comprise aninorganic element with hydrolysable substituents attached to it.

It is possible, for example, to use one or more other hydrolysablecompounds together with the hydrolysable silane(s) containing at leastone epoxide group in component a), the amount of the other hydrolysablecompounds preferably not exceeding 80 mol % and in particular 60 mol %,based on the total amount of hydrolysable compounds employed.

Examples of suitable other hydrolysable compounds include hydrolysablecompounds of elements selected from the third and fourth main groups(especially B, Al, Ga, Si, Ge and Sn) and the third to fifth transitiongroups of the Periodic Table (especially Ti, Zr, Hf, V, Nb and Ta). Itis also possible, however, for other metal compounds to giveadvantageous results, such as compounds of Zn, Mo and W. With particularpreference, these compounds are hydrolysable compounds of elements fromthe group Si, Ti, Zr, Al, B, Sn and V, which are hydrolysed with thehydrolysable silane(s) of component a).

All of these compounds contain hydrolysable groups. As examples,reference may be made to the examples of X that are listed in formula(I). The compounds may also contain nonhydrolysable groups in additionto the hydrolysable groups. Except for Si, however, this is notpreferable. As examples, reference may be made to the examples of R″that are set out below in formula (III). The silanes which can be usedmay have, for example, the following general formula (III):

R″_(n)SiX_(4−n)  (III)

in which n is 0, 1, 2 or 3, preferably 1 or 2, with particularpreference 1, X can be the same or different and is as defined above forformula (I). Examples of nonhydrolysable radicals R″ are alkyl,especially C₁₋₄ alkyl (such as methyl, ethyl, propyl and butyl), alkenyl(especially C₂₋₄ alkenyl, such as vinyl, 1-propenyl, 2-propenyl andbutenyl), alkynyl (especially C₂₋₄ alkynyl, such as acetylenyl andpropargyl) and aryl (especially C₆₋₁₀ aryl, such as phenyl andnaphthyl), it being possible for the groups just referred to to have,where appropriate, one or more substituents, such as halogen and alkoxy.The radicals R″ may also carry functional groups which may, whereappropriate, also be active in crosslinking. Examples of thesefunctional groups are (meth)acryloyl, (meth)acryloyloxy, cyanate,isocyanate, hydroxyl, mercapto, sulphane, thiocyanate and isothiocyanategroups. For example, appropriate mercaptosilanes and isocyanatosilanescan be used which contribute to forming the matrix or which replace apart of the amine-epoxide network by corresponding crosslinking.

Specific examples of these other hydrolysable compounds are: Si(OCH₃)₄,Si(OC₂H₅)₄, Si(O-n- or i-C₃H₇)₄, Si(OC₄H₉)₄, SiCl₄, HSiCl₃, Si(OOCC₃H)₄,CH₃—SiCl₃, CH₃—Si(OC₂H₅)₃, C₂H₅—SiCl₃, C₂H₅—Si(OC₂H₅)₃, C₃H₇—Si(OCH₃)₃,C₆H₅—Si(OCH₃)₃, C₆H₅—Si(OC₂H₅)₃, (CH₃O)₃—Si—C₃H₆—Cl, (CH₃)₂SiCl₂,(CH₃)₂Si(OCH₃)₂, (CH₃)₂Si(OC₂H₅)₂, (CH₃)₂Si(OH)₂, (C₆H₅)₂SiCl₂,(C₆H₅)₂Si(OCH₃)₂, (C₆H₅)₂Si(OC₂H₅₎ ₂, (i-C₃H₇)₃SiOH, CH₂═CH—Si(OOCCH₃)₃,CH₂═CH—SiCl₃, CH₂═CH—Si(OCH₃)₃, CH₂═CH—Si(OC₂H₅)₃,CH₂═CH—Si(OC₂H₄OCH₃)₃, CH₂═CH—CH₂—Si(OCH₃, CH₂═CH—CH₂—Si(OC₂H₅)₃,CH₂═CH—CH₂—Si(OOCH₃)₃, CH₂═C(CH₃)—COO—C₃H₇—Si(OCH₃)₃,CH₂═C(CH₃)—COO—C₃H₇—Si(OCH₂H₅)₃, Al(OCH₃)₃, Al(OC₂H₅)₃, Al(O-n-C₃H₇)₃,Al(O-i-C₃H₇)₃, Al(OC₄H₉)₃, Al(O-i-C₄H₉)₃, Al(O-sec-C₄H₉)₃, AlCl₃,AlCl(OH)₂, Al(OC₂H₄OC₄H₉)₃, TiCl₄, Ti(OC₂H₅)₄, Ti(OC₃H₇)₄,Ti(O-i-C₃H₇)₄, Ti(OC₄H₉)₄, Ti(2-ethylhexoxy)₄; ZrCl₄, Zr(OC₂H₅)₄,Zr(OC₃H₇)₄, Zr(O-i-C₃H₇)₄, Zr(OC₄H₉)₄, ZrOCl₂, Zr(2-ethylhexoxy)₄, andalso Zr compounds which have complexing radicals, such as β-diketone andmethacryloyl radicals, BCl₃, B(OCH₃)₃, B(OC₂H₅)₃, SnCl₄, Sn(OCH₃)₄,Sn(OC₂H₅)₄, VOCl₃ and VO(OCH₃)₃.

As other hydrolysable compounds it is also possible to make use, inaddition or alone, of, for example, hydrolysable silicon compoundshaving at least one nonhydrolysable radical that contains fluorineatoms, in particular from 5 to 30 fluorine atoms, attached to carbonatoms which are preferably separated from Si by at least two atoms.Examples of hydrolysable groups which can be used in this context arethose as indicated for X in formula (I). The use of a fluorinated silaneof this kind additionally confers hydrophobic and oleophobic (dirtrepellency) properties on the corresponding coating. Such silanes aredescribed in detail in DE 4118184.

Where appropriate, nanoscale inorganic particulate solids may also bepresent in the coating composition. Through the use of these solids itis possible, for example, to bring about further increases in thescratch resistance and chemical stability. The nanoscale inorganicparticulate solids may be composed of any desired inorganic materials,but in particular are composed of metals or metal compounds such as, forexample, hydrated or unhydrated oxides such as ZnO, CdO, SiO₂, TiO₂,ZrO₂, CeO₂, SnO₂, Al₂O₃, In₂O₃, La₂O₃, Fe₂O₃, Cu₂O, Ta₂O₅, Nb₂O₅, V₂O₅,MoO₃ or WO₃; chalcogenides such as sulphides (e.g. CdS, ZnS, PbS andAg₂S), selenides (e.g. GaSe, CdSe and ZnSe) and tellurides (e.g. ZnTe orCdTe), halides such as AgCl, AgBr, Agl, CuCl, CuBr, Cdl₂ and PBl₂;carbides such as CdC₂ or SiC; arsenides such as AlAs, GaAs and GeAs;antimonides such as InSb; nitrides such as BN, AlN, Si₃N₄ and Ti₃N₄;phosphides such as GaP, InP, Zn₃P₂ and Cd₃P₂; phosphates, silicates,zirconates, aluminates, stannates and the corresponding mixed oxides(e.g. those having a perovskite structure such as BaTiO₃ and PbTiO₃). Itis possible to use one kind of nanoscale inorganic particulate solids ora mixture of different nanoscale inorganic particulate solids.

The nanoscale inorganic particulate solids preferably comprise an oxide,oxide hydrate, nitride or carbide of Si, Al, B, Zn, Cd, Ti, Zr, Ce, Sn,In, La, Fe, Cu, Ta, Nb, V, Mo or W, with particular preference of Si,Al, B, Ti and Zr. Preferred nanoscale inorganic particulate solids areboehmite, ZrO₂ and TiO₂, and titanium nitride.

The nanoscale inorganic particulate solids generally possess a particlesize in the range from 1 to 300 nm or 1 to 100 nm, preferably 2 to 50 nmand with particular preference 5 to 20 nm. This material can be used inthe form of a powder but is preferably used in the form of a sol (inparticular an acidically stabilized sol).

Particularly when importance is placed on very good properties of highscratch resistance, the nanoscale inorganic particulate solids can beused in an amount of up to 50% by weight, based on the solid componentsof the coating composition. In general, the amount of nanoscaleinorganic particulate solids is in the range from 1 to 40% by weight,preferably from 1 to 30% by weight, with particular preference from 1 to15% by weight.

It is also possible to use nanoscale inorganic particulate solids whichhave addition-polymerizable and/or polycondensable organic surfacegroups. Such addition-polymerizable and/or polycondensable nanoparticlesand their preparation are described, for example, in DE 19746885.

As a further component it is possible, preferably together withcomponent a), for at least one organic monomer, oligomer or polymercontaining at least two epoxide groups, or mixtures thereof, to bepresent. These organic monomers, oligomers or polymers containingepoxide groups comprise, for example, aliphatic, cycloaliphatic oraromatic compounds, aliphatic, cycloaliphatic or aromatic esters orethers or mixtures thereof, based for example on ethylene glycol,1,4-butanediol, propylene glycol, 1,6-hexanediol, cyclohexanedimethanol,pentaerythritol, bisphenol A, bisphenol F or glycerol, each containingat least two epoxide groups. They may also contain more epoxide groups,in the case of monomers or oligomers 3 or 4, for example.

Specific examples include 3,4-epoxycyclohexylmethyl,3,4-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexyl) adipate,cyclohexanedimethanol diglycidyl ether, glycerol triglycidyl ether,neopentyl glycol diglycidyl ether, pentaerythritol polyglycidyl ether,2-ethylhexyl glycidyl ether, 1,6-hexanediol diglycidyl ether,polypropylene glycol diglycidyl ether, epoxy resins based on bisphenolA, epoxy resins based on bisphenol F and epoxy resins based on bisphenolA/F.

The organic monomer, oligomer or polymer containing at least two.epoxide groups is used at most in an amount of 50% by weight, e.g. in anamount of from 15 to 30% by weight, based on components a). The use ofthese compounds containing epoxide groups is not a preferred embodimentbut may be advantageous, for example, on grounds of price.

In the coating composition there may be further additives present whichare normally added in the art depending on end use and desiredproperties. Specific examples include solvents, colour pigments, NIRand/or IR reflecting or absorbing pigments, dyes, UV absorbers,lubricants, such as surfactants, fluorosilanes or graphite, orthermochromic dyes.

The prehydrolysates used as component a) and, where appropriate, ascomponent b) are obtained by hydrolysing the hydrolysable compounds withwater. If desired, hydrolysis may be provided by, for example, heatingor adjustment to an appropriate pH. The hydrolysable radicals of thehydrolysable compounds are replaced in whole or in part by OH groups.During this procedure, condensation reactions may also take place, sothat the prehydrolysates may also contain partial condensation products.Preferably, however, the hydrolysis is conducted in such a way that theprogress of the condensation reaction is slow, with the consequence thatstorable starting components are obtained. Normally and preferably,components a) and b) are prehydrolysed separately from one another andonly then combined. Naturally, however, it is also possible to carry outjoint prehydrolysis of the hydrolysable compounds of components a) andb).

For the hydrolysis it is preferred to use an amount of water which issubstoichiometric; i.e., an amount which is not sufficient to hydrolyseall of the hydrolysable groups present. It is possible, for example, towork with an approximately half-stoichiometric ratio (molar ratio ofhydrolysable groups to H₂O=1:0.6 to 1:0.4).

Following the prehydrolysis and, where appropriate, partialcondensation, components a) and b) are mixed with one another (providedthat they are not hydrolysed jointly). The mixing ratio of component a)to component b) is preferably chosen such that the molar ratio of theepoxide groups present to the amino groups is from 7:1 to 1:1, withparticular preference from 7:2 to 7:3.

After the components have been mixed, condensation and crosslinking takeplace. If desired, this process can be assisted by pH adjustment orheating. Condensation in this context is understood as the linking ofthe silanes (or of the other elements containing hydrolysable groups) byway of the condensation of the —OH groups to oxygen bridges, with theformation, for example, of polysiloxanes (inorganic condensation). Thedegree of condensation of the polycondensate which forms is preferablyfrom 50 to 90%, with particular preference from 60 to 80%, in particularfrom 60 to 70%. Controlling the degree of condensation is known to theperson skilled in the art, and can be carried out, for example, by wayof the amount of water for the hydrolysis. The degree of condensationhere is understood to be the percentage fraction of condensed hydrolysedor hydrolysable groups, relative to the hydrolysed or hydrolysablegroups in the uncondensed state.

Additionally, crosslinking takes place between the epoxide groups andthe amino groups (organic crosslinking). Over the course of time thereis an increase in the degree of crosslinking and in the degree ofcondensation. Then, at a particular point in time, the amino protectivegroup reagent is added. On account of its greater reactivity with theamino groups, it reacts with them to form amine derivatives which arenot amenable to a crosslinking reaction, with the result thatcrosslinking is terminated.

The amino protective group reagent is added in an amount sufficient toderivative the amino groups that have not yet been crosslinked and so toarrest the crosslinking reaction. The point in time of its addition ischosen such that the degree of crosslinking of the resultantpolycondensate, expressed as the percentage fraction of the crosslinkedamino groups and epoxide groups relative to amino groups and epoxidegroups in the uncrosslinked state, is from 5 to 50%, preferably from 10to 50%, in particular from 20 to 40%. The amino protective group reagentis normally added from several minutes to several hours after combiningcomponents a) and b). Because of the acidity of the amino protectivegroup reagent, the pH may fall when it is added.

The determination of the degrees of condensation and crosslinking isknown to the person skilled in the art. The determination of theconcentrations of the relevant components present in the polycondensate,and hence of the degrees of crosslinking and condensation, can becarried out, for example, by means of NMR measurement, followingcalibration with the starting substances. This allows the progression inthe degrees of crosslinking and condensation to be monitored over time.

Where appropriate, inert solvents may be added to the compositions atany stage in their preparation for the purpose of adjusting therheological properties. These solvents are preferably alcohols and/oralcohol ethers which are liquid at room temperature, examples beingC₁-C₈ alcohols, which, moreover, are also formed during the hydrolysisof the alkoxides of the elements in question that are used withpreference, or monoethers of diols such as ethylene glycol or propyleneglycol with C₁-C₈ alcohols.

Preferably, following the addition of the amino protective groupreagent, a polycondensate is obtained which has a degree of crosslinkingof from 5 to 50% and preferably also has a degree of condensation offrom 50 to 90%. This polycondensate may be used, where appropriatetogether with further customary additives, as a coating composition.

The substrate to be coated may, for example, be a substrate made ofglass, ceramic, glass ceramic, plastic, metal or wood. It is preferablya substrate made of glass, ceramic or glass ceramic. Particularadvantages are achieved in accordance with the invention using glasssubstrates, e.g. flat glass or hollow glassware. Practical examplesinclude lightweight disposable hollow glass bottles, thin glass (d≦1 mm)for displays, solar cells and solar collectors.

The substrate may have been pretreated. Where appropriate, the substratehas already been provided with customary primers or coatings.

The coating composition of the invention is applied to the substrate bytechniques known from the prior art. Application may take place by meansof standard coating techniques, such as dipping, spreading, brushing,knife coating, rolling, spraying or spin coating, for example. In onepreferred embodiment, the substrate, especially glass, is heated beforeapplication, to 80° C. for example. Where appropriate, initial partialdrying at room temperature (partial removal of the solvents present) isfollowed by thermal treatment or consolidation, at temperatures forexample of 80° C.-150° C., preferably at 100° C.-130° C., withparticular preference at about 120° C.

The coat thickness of the coating composition applied to the substrateand heat-treated can be for example from 15 to 45 μm, preferably from 25to 40 μm and in particular from 30 to 35 μm.

The coatings can if desired have high transparency and are also notablefor high scratch resistance. In particular, a hard but elastic behaviourof the coating produced is obtained which is sufficient for maintenanceof strength, so that an increase in the (fracture) strength ismaintained even after stress.

The examples which follow are intended to illustrate the presentinvention but without restricting its scope.

EXAMPLE 1

Strength-maintaining coating on float glass 2 mm thick (sol 4)

Synthesis and coat application of the coating sol In a three-neckedround-bottomed flask with reflux condenser and dropping funnel, 51.4 gof distilled water were added to 450 g of3-glycidyloxypropyltrimethoxysilane (GPTS) and the mixture was heated toboiling under reflux for 24 h (molar ratio —OR:H₂O=1:0.5). 49 g of waterwere added at room temperature with vigorous stirring to 388 g ofaminopropyltriethoxysilane (APTES) (molar ratio —OR:H₂O=1:0.5). 50 ml ofisopropanol and 50 g of the APTES prehydrolysate were added withstirring to 185 g of the GPTS prehydrolysate. After a stirring time of20 minutes, 4.7 ml of acetic anhydride were added to this sol. Thefloatglasses (100 mm×100 mm×2 mm) were coated by dipping. The coats wereconsolidated in a drying oven at 120° C. for 10 minutes. Following thiscoating operation, the floatglasses were damaged with the aid of a sandtrickle unit (in accordance with DIN 52 348) with 500 g of corundum ofparticle grade P 30. The fracture strength of the coated and damagedglasses was subsequently determined in a double ring bending test. Theresults were evaluated using Weibull statistical analysis. Thestrength-maintaining effect was tested in comparison with uncoated anddamaged glasses. The damaged and undamaged glasses were analysed usingwhat are called Weibull plots.

It is seen that the fracture strength of the uncoated flat glass isgreatly impaired; for example, there is a reduction from 628 MPa(566-698 MPa) to 57 MPa (55-59 MPa), whereas the strength of the glasswith the coating of the invention remains at the high level.

EXAMPLE 2

Strength-maintaining coating on hollow glassware

The coating sol was synthesized as in example 1. Coat application to the1 l soft drink bottles tested was likewise carried out by dipcoating.The fracture strength of the bottles was determined by means of abursting pressure instrument. In order to simulate realistic damage, thebottles were damaged using a line simulator of different times (5 min, 7min and 15 min) and conditions (dry, wet). Following this damage, thebursting pressure strength was determined.

It was found that the bursting pressure strength of the bottles isincreased by 35% as a result of the coating process, and is alsomaintained at this high level after 15 minutes of simulated lineconditions (dry), whereas the bursting pressure strength of uncoatedbottles has fallen to about 55% of the original value after just 5minutes of simulated line conditions. The results for simulated wet lineconditions (dripping water) are similar.

What is claimed is:
 1. A coating composition comprising a polycondensateobtained by reacting components: (a) a prehydrolysate based on at leastone hydrolysable silane having at least one non-hydrolysablesubstituent, the silane containing one or more epoxide groups on atleast one non-hydrolysable substituent (an epoxide-containing silane);(b) at least one amine component selected from at least one of: (1) aprehydrolysate based on at least one hydrolysable silane having at leastone non-hydrolysable substituent, the silane containing one or moreamino groups on at least one non-hydrolysable substituent (anamino-containing silane), and (2) an amine compound containing at leasttwo amino groups; and (c) an amino group protective reagent; where adegree of crosslinking of the polycondensate, expressed as a percentagefraction of crosslinked amino groups and epoxide groups relative toamino groups and epoxide groups in the uncrosslinked state originallypresent in components (a) and (b), is from 5% to 50%.
 2. The coatingcomposition of claim 1, wherein the polycondensate has a degree ofcondensation of from 50% to 90%.
 3. The coating composition of claim 2,wherein component (b) comprises (1).
 4. The coating composition of claim1, wherein component (b) comprises at least 60 mol-% of (1).
 5. Thecoating composition of claim 1, wherein a molar ratio of the epoxidegroups to the amino groups is from 7:1 to 1:1.
 6. The coatingcomposition of claim 1, wherein the epoxide-containing silane comprisesa compound of formula X₃SiR in which each X is independently ahydrolysable group and R is a glycidyloxy-(C₁-C₆)-alkylene group.
 7. Thecoating composition of claim 1, wherein component (b) comprises aprehydrolysate based on an amino-containing silane of formula X₃SiR′ inwhich each X is independently a hydrolysable group and R′ is annon-hydrolysable radical which contains at least one primary orsecondary amino group.
 8. The coating composition of claim 7, whereinthe epoxide-containing silane comprises at least one ofglycidyloxypropyl trimethoxysilane and glycidyloxypropyltriethoxysilane.
 9. The coating composition of claim 8, wherein theamino-containing silane comprises at least one of aminopropyltrimethoxysilane and aminopropyl triethoxysilane.
 10. The coatingcomposition of claim 1, wherein the polycondensate comprises a reactionproduct of components (a) through (c) and of at least one of an organicmonomer, oligomer and polymer which contains at least two epoxy groups.11. The coating composition of claim 1, wherein the polycondensatecomprises a reaction product of components (a) through (c) and of atleast one hydrolysable compound of at least one of Si, Ti, Zr, Al, B,Sn, and V, which compound is different from the epoxide-containingsilane and the amino-containing silane.
 12. The coating composition ofclaim 1, wherein component (c) comprises at least one of an acidanhydride and an acid halide.
 13. The coating composition of claim 12,wherein component (c) comprises at least one of acetic anhydride andacetyl chloride.
 14. The coating composition of claim 1, wherein thecomposition further comprises at least one of a color pigment, an NIRreflecting pigment, an NIR absorbing pigment, an IR reflecting pigment,an IR absorbing pigment, a dye, a UV absorber, a lubricant, a nanoscaleinorganic particulate solid, and a thermochromic dye.
 15. A process forpreparing a coating composition, comprising: (A) mixing components: (a)a prehydrolysate based on at least one hydrolysable silane having atleast one non-hydrolysable substituent, the silane containing one ormore epoxide groups on at least one non-hydrolysable substituent; and(b) at least one amine component selected from at least one of: (1) aprehydrolysate based on at least one hydrolysable silane having at leastone non-hydrolysable substituent, the silane containing one or moreamino groups on at least one non-hydrolysable substituent, and (2) anamine compound containing at least two amino groups; and (B)subsequently adding and mixing component (c) an amino group protectivereagent; a time of adding and mixing component (c) being such that adegree of crosslinking of a resultant polycondensate, expressed as apercentage fraction of crosslinked amino groups and epoxide groupsrelative to amino groups and epoxide groups in the uncrosslinked stateoriginally present in components (a) and (b), is from 5% to 50%.
 16. Theprocess of claim 15, wherein the polycondensate has a degree ofcondensation of from 50% to 90%.
 17. The process of claim 16, whereincomponent (b) comprises (1).
 18. The process of claim 15, whereincomponent (b) comprises at least 60 mol-% of (1).
 19. The process ofclaim 18, wherein a molar ratio of the epoxide groups to the aminogroups is from 7:1 to 1:1.
 20. A method of coating a substrate selectedfrom glass, glass ceramic, ceramic and plastic, comprising the substratewith the coating composition of claim
 1. 21. A substrate coated with thecoating composition of claim
 1. 22. A substrate comprising a coating,wherein the coating is derived from a coating composition apolycondensate obtained by reacting components: (a) a prehydrolysatebased on at least one hydrolysable silane having at least onenon-hydrolysable substituent, the silane containing one or more epoxidegroups on at least one non-hydrolysable substituent (anepoxide-containing silane); (b) at least one amine component selectedfrom at least one of: (1) a prehydrolysate based on at least onehydrolysable silane having at least one non-hydrolysable substituent,the silane containing one or more amino groups on at least onenon-hydrolysable substituent (an amino-containing silane), and (2) anamine compound containing at least two amino groups; and (c) an aminogroup protective reagent; and wherein the coating has a thickness offrom 15 μm to 45 μm.
 23. The substrate of claim 22, wherein thesubstrate comprises at least one of glass, glass ceramic, ceramic andplastic.
 24. The substrate of claim 22, wherein the substrate comprisesflat glass.
 25. The substrate of claim 22, wherein the substratecomprises hollow glassware.